Cytolytic T lymphocytes are activated as a result of T cell receptor recognition of foreign peptide complexed to class I MHC proteins. It is clear, however, that effective activation of the CTL also involves interactions of 'accessory' proteins on the CTL (including CD8, LFA-1 and VLA's) with ligands on the antigen-bearing cell. Using artificial membranes having well defined and easily varied ligand compositions, considerable progress has been made in defining the qualitative and quantitative contributions that these interactions can make to activation of immediate responses (eg. degranulation) by cloned effector CTL. Proposed studies will extend this approach to systematically assess the relative roles of the accessory interactions and lymphokines in activating CD8+ precursor CTL for proliferation and differentiation to effector CTL. In addition, the requirements for activating naive versus primed (in vivo) precursor CTL clearly differ, and studies will be done to determine if this results from differences in ligand interaction requirements, cytokine requirements, or both. Both allogeneic and self-restricted, peptide specific CTL responses will be studied. Antigen-bearing artificial membranes have been found to significantly affect in vivo generation of CTL responses. Administration of antigen in this form does not result in a detectable CTL response, but administration to mice along with live, antigen-bearing cells results in a dramatic augmentation of the response compared to that obtained in mice receiving only stimulator cells. Augmentation does not simply result from increased antigen load; the effect is unique to antigen on cell-size artificial membranes and appears to occur at the level of precursor CTL activation. The ability to significantly augment CTL response levels has implications for tumor and virus disease therapy, and experiments examining cytolytic responses to syngeneic tumors, and effects on tumor growth and host survival, have demonstrated the potential of this approach. In the proposed project, the requirements for in vivo stimulation/augmentation will be studied in parallel with the in vitro activation studies described above. Studies are also proposed to determine the mechanism(s) by which antigen-bearing artificial membranes are able to uniquely modulate in vivo response levels. It is anticipated that these experiments will provide insight into the parameters which influence the in vivo generation of CTL responses, and suggest approaches for prevention and therapy of diseases.